Frequency and phase modulation detector



Sept. 27, 1949.- H. GOLDBERG 2,483,195

FREQUENCY AND PHASE MODULATION DETECTOR Filed. April 28, 1947 RADIO FNTERMEDIATE FREQUENCY CONVERTER FREQUENCY AMPLIFIER AMPLIFIER 1 HAROLD GOLDBERG Patented Sept. 2?, 1949 FREQUENCY AND PHASE MODULATION DETECTOR Harold Goldberg, Towson, Md., assignor to Benf v Q dix Aviation Corporation, Towson, Md., a cor poration of' Delaware Application April 28, 1947, Serial No. 744,502

11 Claims.

This invention is directed to frequency-modulation receivers, and more specifically, it is directed to a novel receiver for the detection of frequency or phase modulated radio signals.

One of the reasons for the wide use of frequency-modulation in radio communication is of installations, and, the use of FM has to some extent been avoided because of this shortcoming.

It is an object of this invention to provide an FM receiver having automatic gain control.

It is a further object of this invention to provide an FM receiver which suppresses amplitudemodulation disturbances without the use of an amplitude limiter. v I v i a It is a further object of this invention to eliminate one or more of the shortcomings of the prior art arrangements.

The above and further objectsand advantages of this invention are provided by an AM receiver having an AVC characteristic which is proportional to the frequency of the incoming signal.

The above and further objects and novel features will more full appear from the following detailed description when the same is read in connection with the accompanying drawing wherein there is illustrated a diagram of a receiver in accordance of ,the instant invention Referring now to the drawing, there is illustrated an antenna .lflconnected to the input circuit of a radio frequency amplifier H. The output of the amplifier] I is. connected through a frequency converter l2 ,to the input circuit of an intermediate frequency am 'plifier l3 the output of which is connected to the control electrode of a vacuum'tube l4 and to the cathode of a second vacuum tube l5. V U

The anode of the tube is connected to a source of voltage +B through a circuit l6 comprising the parallel combination of an inductor and a condenser, and to the anode of a tube I! through a condenser I8. The anode of the tube 11 is connected to ground through a resistor I9, and through a resistor 20 to an AVC bus 2|. The AVC bus 2| is connected to ground through a condenser 22.

The cathodes of the tubes l4'jand I! are connected to ground. The anode of the tube I is connected to ground through a parallel circuit v 23 comprising a resistorjlandacondenser, and to an output terminal 24.

The amplification or gain of the R. F. amplifier ii, the converter l2, and the I. F. amplifier 13 is controlled byltheir connection to the AVG bus 2|.

V In operation an input signall Ei which is either frequency or phase modulated, and which may also be amplitudernodulated by noise or the like, is applied to the input circuit of the amplifier H from the antenna in. For convenience we may lump thejgain characteristics of the stages preceding the tube I l as:

' resistor for the tube l1 across which the AVG is developed. The resistor iii-and the condenser 22 serve as a filter to provide the AVG circuit the propertime constant, 7 V I The output voltage. of the slope-detector- AVG-filter combination 6. isrelated to the I. F.

signal E0 fed to the cathode ofthe tube l5 as follows: 1 r

Eo=signa1 potential at the output of the I. F.

d=6/E'o at the mean signal frequency.

L(Af) =a function of frequency expressive of the influence ofth'eislope circuit IS on the ratio e/Eo as the frequency is Varied by an increment A from'the mean.

Where L (Af)"}is a function of the'deviation of the frequency of E0 from its: center frequency.

The output voltage e of the slope detector varies the gain of thestages preceding the tube M in accordance with'the product of (1) and Equation 5 shows that the voltage applied to the cathode; of the tube ,l5, which may now be identified as a second detectorhaving a load circuit 23' and an output terminal 24,, an amplitude modulated signal whose modulation envelope may be a linear function of the frequency deviation. By properly choosing L(Af) this condition may be fulfilled, and the use of a conventional AM second detector Wis justified.

Since El, the input voltage, does not appear in Equation 5 it will be manifest. as long. as Equation 4 is satisfied, amplitude: modulation components of E1 will be rejected.

What is claimed is:

1. A receiver for the reception of an angle modulated signal comprising: means constituting an amplifying channel having substantially uniform transmission. characteristics over abandof frequencies including thef-requenciesi of. said. signal; a frequency selective automatic gain control system having different transmission characteristics at each frequency insaidl band; means: applying the output of said channel to the'input of said system; means applying the output of said system to modulate the gainof' said channel as a, function of" the angle modulation of said signal; and". an amplitude responsive detector re.- ceiving. the output of said channel.

2. A receiver for the receptioncf an angle mod.- ulated signal comprising: an amplifier having substantially uniform transmission characteristics over a band of; frequencies including the frequencies of said signal; a frequency selective automatic ain control system having incorporated as a transmission path therein a circuit resonant at one of the ofsaid band: means applying theoutput ofsaidamplifierto the input of said system and means applying the output of said system to modulatethegaim of said amplifier as a functionof the angle modulation of said signal; and an amplitude responsive detector receiving the output of said: amplifier;

3. A receiver for reception of an angle modulated signal comprisinga' an amplifier having substantially uniform transmission characteristics over a band of frequenciesincluding'the frequencies of said signal; a frequency selective automatic gain control system having incorporated as a transmission path therein a circuit resonant outside of, but adjacent to, one of the limits of said band? means applying the output of said amplifier to the input of said system, means applying the output of said system to modulate the gain of saith amplifier as a: function of the angle modulation of said signal; and an amplitude responsivedetector receiving the output of said amplifier.

4. A receiver for the reception of an angle modulated signal comprising: means constituting an amplifying channel havingsubstanti'ally uniform transmission. characteristics over a band of frequencies including the frequencies. of said signal; an amplifier having an output circuitresonant at a frequency adjacent said. band: of frequencies; means applying; the output. of said channel to the input of said amplifier; means for the amplitude detection of the output of said amplifier; means applying the output of said detector to modulate the gain of said channel; and an amplitude responsive detector receiving the output of said. channel.

5. A receiver for the reception of an angle modulated signal comprising: means constituting an amplifying channel having substantially uniform transmissioncharacteristics over a band of frequencies including the. frequencies of, said signal; means varying. thegain. of saidamplifying means as a function of the angle. modulation of '4 said signal; and means. recovering the envelope of the resultin amplitude modulated signal.

6. A receiver for the reception of an angle modulated signal comprising: means constituting an amplifying channel having substantially uniform transmission characteristics over a band of frequencies including the frequencies of said signal; means varying the gain of said amplifying means as a function of the angle modulation of saidsigna-land inversely with variations of the amplitude of said signal; and means recovering the envelope of the resulting amplitude modulated; signal.

7. The method of receiving an angle modulated signal which comprises submitting; the said signalto amplification. uniformly over the range of frequencies encompassed. thereby; submitting said amplified signal. to frequency selective am.- plification. which varies linearly through. said range of frequencies; utilizing said. frequency selectively amplified signal to modulate the: said uniform amplification as. a function of the frequency of, said signal; and; recovering the envelope of the. resulting amplitude modulated signal.

8. The method of. receiving, an angle. modulated signalwhichcomprises; submitting the said signal toamplification uniformly over the range of frequencies encompassed thereby; submitting said amplifiedsignaltoamplification. which varies as a function of the, frequency thereof; utilizing the product of said frequency varied. amplification to modulate the said uniform amplification; and recovering. the envelope of the; resulting amplitude modulated signal.

9. The method, of receiving an. angle modulated signal which comprises submitting the said signal to amplification uniformly over the range of frequencies encompassed thereby; submitting said amplified signallto. frequency detection; applyin the product of. said frequency detection to modulate the said uniform; amplification and recovering. the envelope. of the resulting amplitude modulated.

10. The method of receiving. an angle modulated signal whichcomprisesz. submitting; the said signal to amplification; uniformly over. the. range of frequencies encompassed thereby; recovering from saidsignal so amplified a. voltagervarying in amplitude with said angle modulation and varying inversely with amplitude; variations of said signal; modulating said uniform amplification with said voltage and recovering the envelope of the resulting. amplitude modulated signal.

11. The method: receiving an angle mod-ulated signal which comprises: submitting. the-said signal to amplification uniformly over the range of frequencies encompassedthereby; submitting said amplified signal to: amplification which varies as a function of thefrequency thereof; recovering the envelope of the product of said frequency varied amplification; modulating said uniform amplification: with said. envelope; and recovering the envelope of; the resulting amplitude modulated signal.

HAROIDGOLDBERG..

REFERENCES. CITED The following: references are of record in the fileof this patent STATES: PATENTS Wheeler Mar. 281.. 1 939:

Disclaimer 2,483,195.-Hmrold Goldberg, Towson, Md. FREQUENCY AND PHASE MODULA- TION DETECTOR. Patent dated Sept. 27, 1949. Disclaimer filed June 6, 1951, by the assignee, Bendix Aviation Corporation. Hereby enters this disclaimer to claims 1, 5, 6, 7, 8, 9, 10, and 11 of said patent.

[Oficz'al Gazette August 11;, 1951.] 

